The invention relates to a method for operating a contactless and batteryless chip card in accordance with the preamble of claim 1. Furthermore, the invention relates to an array for implementation of the method.
Contactless and batteryless chip cards are known from, for example, Winfried Wigand "Die Karte mit dem Chip", Siemens Nixdorf Informationssysteme AG, Berlin and Munich, 1991, pages 34-36. The energy is supplied by transformer connection via an alternating field with a write/read unit. The alternating field is generated by this write/read unit. Data transmission from and to the chip card is achieved by modulation of this alternating field. A suitable method is described in DE 41 07 311 A1. On the chip card, modulation of the alternating field is effected during reading access by a connected load that damps the antenna coil. Amplitude modulation is used as the modulation type, and can be combined with other modulation methods.
The chip card known from the aforementioned patent application contains a voltage detector for detection of blanking gaps in the alternating field. The voltage detector is supplied with the voltage generated by the antenna coil. The precise function of the voltage detector is not described there. Generally speaking, however, a circuit array, for example amplifier and comparator, is necessary to process the analog signal in order to generate the required output signal.
The known arrays do however have the drawback that a large amount of circuitry is necessary for the voltage detector to operate dependably even at supply voltages of around 1 volt.